FIGS. 4 and 5 depict two known circuit breakers of the above-mentioned type. Referring first to FIG. 4, inside an insulating case 1 that is divided into two portions, there are provided a contact apparatus 20 which constitutes a portion of cable way, a switching mechanism 30 for opening/closing the contact apparatus 20, an overcurrent trip apparatus 40 connected in series to the contact appartus 20 for disconnecting the contact apparatus 20 via the switching mechanism 30 when the current of the cable way becomes excessively high.
The insulating case is generally made of phenol aldehyde resin. To each of the facing portions of the insulating case 1, there are formed an arc-extinguishing space 1a above the contact parting area of a fixed contact 11 and a movable contact 12 (right side in the figure), which constitute the contact apparatus 20. To the upper portion of the arc-extinguishing space 1a there is provided an air exit 1b that is covered with a mesh plate 2 in order to prevent an invasion of foreign materials. To the back face side of the arc-extinguishing space 1a (lower side in the figure) there is provided a guide slot 1c in which the fixed contact 11 is to be fixed. On the facing inner walls of the arc-extinguishing space 1a, respectively, is formed an insulating coat 3 of high arc resistance epoxy resin or the like in order to prevent deterioration of the insulation between the contacts due to carbonization of the surfaces by arcing generated upon opening of the contact apparatus 20. Referring now to the circuit breaker of FIG. 5, the difference compared with the above-mentioned circuit breaker is that as means for preventing the deterioration of insulation between contacts by arcing generated upon circuit-breaking, there is provided an insulating collar 5 that is formed by folding fiber or the like into a gate shape and fitting the fiber from around the arc-extinguishing space 1a by means of reinforcing metal 4.
In such conventional circuit breakers, the insulating coat 3 must be applied manually which is inefficient and requires considerable waiting time between coating and desiccation. The insulating collar 5 needs to be fixed by the reinforcing metal 4 in order to avoid deformation and displacement thereof, which is costly.